1. Field of the Invention
This invention relates to a grinding machine and dresser therefor for dressing a rotatable grinding wheel of the machine with a cutting profile that grinds a crooked configuration in a workpiece.
2. Description of the Prior Art
Grinding machines include rotatable grinding wheels that are formed from abrasive particles secured to each other by a bonding agent. As the wheel is rotated, each abrasive particle that engages the workpiece to be ground acts as a miniature cutting tool with irregular inefficient cutting angles, producing extremely small, highly deformed chips. Because of the small size of cut and the small chips, the surface finish is good and precise tolerances can be maintained. After being subjected to various amounts of use, grinding wheels wear as the abrasive particles become unbonded at the cutting profile of the wheel which engages the workpiece. To regain the precise tolerances with a used wheel, dressers are utilized with grinding wheels to dress the cutting profile to its original configuration.
When grinding wheels have a cutting profile for grinding a crooked configuration having straight line bends and/or arcuately curved portions, the dressers utilize pointed cutting tools to dress the wheel. The cutting tool normally has a diamond at its point which is engaged with the rotating wheel to provide the dressing. The cutting tool is mounted by a holder which is moved in accordance with the movement of a follower that follows a template mounted on the dresser. The template normally has the profile of the ground workpiece and faces the cutting wheel in an opposed relationship so that the template profile is the reverse image of the grinding wheel cutting profile which is the reverse image of the configuration ground into the workpiece. By way of example, if the workpiece is to be ground with a toothed configuration, the template normally has a toothed profile like that to be ground into the workpiece and is mounted on the dresser in an opposed relationship with respect to the cutting profile of the grinding wheel. Therefore, when the follower is engaged with the tips of the template teeth, the cutting tool is dressing the wheel in the valleys between the teeth of the cutting profile of the wheel. Likewise, the follower is engaged with the valleys between the template teeth while the cutting tool is dressing the tips of the cutting profile on the wheel. When there is a particularly steep angle to the toothed configuration to be ground, the follower is subjected to lateral forces as it is engaged with the valleys between the template teeth. The cutting tool is then being moved in accordance with the follower movement to dress the tips of the teeth on the cutting profile of the wheel, these tips being the wheel portions that grind the valleys between the teeth ground into the workpiece. The lateral forces can cause problems in maintaining the desired tolerances in the toothed configuration ground into the workpiece.
A grinding wheel must be moved in relation to the workpiece after being dressed in order to maintain the same depth of cut before and after dressing. The movement of the wheel must be equal to the change in its radius during dressing. Usually, the dresser is mounted on the opposite side of the wheel from the workpiece in a 180.degree. relationship. Consequently, the dresser must be moved twice as far as the wheel in order to maintain the proper positioning of the wheel and the dresser so there is the same cutting depth in the workpiece before and after dressing. In the past, this movement of the wheel and dresser has been accomplished by a drive screw that has first and second threaded portions spaced axially along its length. One of the threaded portions has a pitch twice as great as the other and drives the dresser, while the other threaded portion of lesser pitch drives the grinding wheel. The rotation of the drive screw thus maintains the proper spaced relationship between the grinding wheel and the dresser since the greater pitch of the dresser screw portion moves it twice as far as the wheel for a given amount of screw rotation.